Semiconductor opto-electronic packaging typically requires multiple devices/subassemblies to be solder-bonded to each other in a stack. For example, in the case of a typical semiconductor active device, the semiconductor laser diode chip is mounted on an intermediate substrate to form what is typically referred to as a hybrid. This hybrid is then mounted on a submount, which is in turn typically mounted on some sort of pedestal or thermo-electric cooler, for heat control in the module, such as a butterfly or DIP package. More recently, more integrated systems have been proposed in which multiple optical components are mounted on a single optical bench-submount.
Typically, each of these devices/ subassemblies is solder bonded to each other. The advantage of solder bonding is its high temperature stability as well as its long-term performance characteristics.
Generally, to create good solder bonds, especially at lower temperatures, flux is used to facilitate surface wetting by the molten solder. The use of flux, however, can lead to problems especially in applications utilizing high-power, active devices. Flux is an organic compound; and organics within the sealed module can decompose, especially at the exit facet of semiconductor lasers, for example. This leads to the deposition of carbon on the laser exit facet, which can result in excessive heat concentration, leading to catastrophic optical damage (COD). Thus, in manufacturing, after solder bonding, any remaining flux must be rigorously flushed from the module prior to lid sealing.
The present invention concerns an optical bench, or submount, tinning/pre-tinning jig. It is useful for solder coating submounts/benches and attaching optical components to the benches in solder reflow ovens, especially using solder preforms, solder coated components, or predeposited solder on the benches.
In general, according to one aspect, the invention features an assembly fixture for optical benches. The fixture comprises a jig base having at least one blind hole. The jig base is formed with a surface that is a non-wetting to solder material. The blind hole is shaped and sized in response to dimensions of the optical bench.
In a preferred embodiment, the fixture further comprises a bench jig shroud. This shroud at least partially covers optical benches installed in the blind holes. The blind holes have at least two opposed tool insertion notches. In one implementation, the depth of the blind hole is approximately one-half the thickness of the optical bench. Preferably, provisions are made in the top of the jig base at the interface with the jig shroud to facilitate its stable placement on the base. The jig shroud includes one or more through-holes to enable access to a top surface of the bench installed on the base.
In general, according to another aspect, the invention can also be characterized in the context of an assembly process for an optical bench. The process comprises the placement of an optical bench in the blind hole. A solder preform is placed between the bench and the jig base. The jig with the optical bench is then heated in a solder reflow oven so as to melt the preform so that the solder is deposited on the underside of the bench when the bench is thereafter cooled.
In some embodiments, optical components, such as components requiring only low precision placement are installed on the optical bench prior reflow. Thus, in one reflow cycle, the bottoms of the benches are solder coated and optical components are installed on the bench top surfaces.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.